Electric valve protective system



arch i, 193. F. MERTENS 2,109,65

ELECTRIC VALVE PROTECTIVE SYSTEM Filed Dec. 7, 1954' Patented Mar. 1, 1938 l'i'E it! S ELECTRIC VALVE PROTECTIVE SYSTEM Switzerland Application December 7, 1934, Serial No. 756,409 In Germany December 8, 1933 14 Claims; 7 (Cl. 175-363) This invention. relates in general to electric valve protective systems, and more particularly to-systerns for preventing the occurrence of disturbances in an electric valve during establishment of the conductive condition of the cathode of the valve by means of an ignition electrode,-

Electric valves of the type in which the cathode is maintained in conductive condition by the .flow of an excitation discharge therethrough, are generally brought into the conductive condition by means of an ignition electrode momentarilyengaging with the cathode. During operation of the Valve, the discharge therein may be momen tarily interrupted, so that the cathode loses its conductivity and the ignition electrode must be operated to reestablish the conductive condition. If the main electrodes of the valve are connected with the associated source and with the load circuit at such time, a circuit may be established from a main anode of the valve to the cathode by way of the ignition electrode and of the energizing circuit therefor, and a flow of Working current may occur through such a circuit with the result that the apparatus connected therein may be damaged or even destroyed. Itis therefore necessary to delay the flow of current through the main anodes of the valve until after the ignition operation of the valve has been com-- pleted, such result being preferably obtained by employing control electrodes operable to prevent the flow of current through the associated anodes. Such control electrodes are preferably so energized that the flow of current through the valve is then released at a gradually increasing voltage to avoid the voltage surge resulting from the sudden impression of full voltage on the load, which may be detrimental to loads of certain particular types.

It is, therefore, one of the objects of the present invention to provide an electric valve protective system by which the control electrodes of the valve neutralize the conductivity of the valve when the excitation discharge thereof is not established.

Another object of the present invention is to provide an electric valve protective system by which the valve is made non-conductive upon failure of the excitation discharge thereof.

Another object of the present invention is to provide an electric valve protective system by which the flow of current through the valve is established at a gradually increasing voltage after interruption of the operation of the valve.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing, which diagrammatically illustrates one embodiment of the present invention applied to theprotection of an electric valve utilized in an alternating current rectifying system.

Referring more particularly to the drawing by characters of reference, reference numeral 2 generally designates an electric valve utilized for controlling the flow of current between an alternating current line 3 and a direct current line l. It will be understood, however, that the nature of the working circuits connected with the valve is immaterial for the present invention, so that the valve maybe utilized for other purposes than for the rectification of alternating current. In the present embodiment, valve 2 is connected with line 3 through a transformer t, the connection between line 3 and. transformer 6 preferably including a circuit breaker l. Valve 2 is provided with a plurality of main anodes 8 severally connected with the phase portions of the secondary winding of transformer 4, and with a cathode 9 connected with one of the conductors of line 4. Cathode Q preferably consists of a body of liquid mercury, which is brought to conductive condition by momentary engagement thereof with an transformer l2 energized from line 3 through a switch it. After a cathode spot is thus established on cathode 9, the cathode is maintained in conductive condition by the flow therethrough of an excitation discharge from excitation anodes it connected with transformer it through resistors Ill.

The engagement of electrode l with cathode 9 is obtained by the action of a solenoid it acting against a spring ii. The solenoid is energized from transformer l2 through the contacts of a relay i8. Ignition electrode ll receives current from transformer l2 through contacts 20 of another relay l9 and through a resistor 2|, the circuit being completed through cathode 9, coils of relays l8 and I9, and a reactor 22 to a midtap of thesecondary winding of transformer E2. The coil of relay i8 is so dimensioned as to cause operation of the relay upon establishment of a flow of current through electrode H, and the coil of relay i9 is so dimensioned as to cause operation of the relay only upon flow therethrough of the considerably larger current of excitation anodes I l.

The operation of each main anode 8 is controlled by means of an associated control electrode '23 which may be energized in any suitable ignition electrode ll receiving current from a manner known in the art. Each control electrode is preferably connected through a resistor 24, with one of the phase portions of the secondary winding 2? of a transformer 26 having a primary winding 28. Winding 21 is connected in star to form a neutral point normally maintained at a negative potential with respect to the potential of cathode 9 by means of a suitable source of negative unidirectional voltage such as a battery 29. The battery may be connected directly between the neutral point and the cathode, or such connection may be effected through a voltage divider 3 Battery 29 may be disconnected from the circuits energized therefrom by means of a switch 32 preferably connected with switch l3 so that those switches must be simultaneously closed.

Winding 28 is preferably connected with line 3 through a step-down insulating transformer 33 and through impedance means such as resistors 34, the purpose of which will appear hereinafter. Each phase of line 3 also supplies, through a resistor 34, the working winding of a reactor 35 having a saturating winding 36. The several windings 36 receive current from voltage divider 3| through contacts 31 of relay It, a resistor 38, contacts 39 of a relay 4|, and through an electric valve 42 of the discontinuous control type having a cathode connected at an intermediate point of voltage divider 3|. Valve 42 is provided with a control electrode connected with the positive terminal of voltage divider 3| through a resistor 43 and through contacts '44 of relay IS. The coil of relay 4| is connected with contacts 3'! of relay 9 and is connected with an intermediate point of resistor 38 through contacts 46 of the relay 4|. Contacts 46 are arranged to close before contacts 39 are opened as a result of the operation of relay 4|. Voltage divider 3| and contacts 44 are bridged by a resistor 4? in series with another resistor 48 receiving unidirectional current from a current transformer 49 inserted in the connection between line 3 and transformer 6, such current being rectified by suitable rectifying devices 5|. Relay I9 is provided with further contacts 52 connecting voltage divider 3| with the closing coil 53 of circuit breaker The circuit breaker may be maintained in the closed position by means of a latch maintained in engagement by means of a low-voltage trip coil 54 energized from line 3 through switch 3.

In operation, the system being connected as shown and line 3 being energized, valve 2 is put in operation by closure of switches l3 and 32. Upon closure of switch 32 the control electrode of valve 52 receives a negative potential with respect to the potential of the associated cathode as a result of the connection thereof with voltage divider through resistors 43, 41 and 48. Such potential is, however, overcome by the positive potential impressed on the control electrode from voltage divider 3| through contacts 44, so that valve 42 becomes conductive. A flow of current is thus initiated from the positive terminal of voltage divider 3| through contacts 31, windings 36, resistor 38, contacts 39 and valve 42 to voltage divider 3|. Such flow of current through windings 36 causes the cores of reactors 35 to become saturated, so that the working windings of the reactors draw comparatively large currents from line 3 through resistors 34. Such flow of current causes a comparatively large voltage drop in resistors 34, with the result that the voltages of the several portions of winding 21,

induced therein from winding 28, are caused to lag and to decrease in value to an extent such that their amplitude becomes less than the value of the unidirectional voltage impressed between cathode 9 and the neutral point of winding 21. The control electrodes 23 are thus maintained at variable negative potentials with respect to cathode 9, and prevent any flow of current through anodes 8 even if circuit breaker I is closed and cathode 9 is made conductive.

At the same time, closure of switch l3 has caused transformer I2 to become energized, and the transformer supplies current to solenoid |6 through the contacts of relay l8. The solenoid accordingly urges ignition electrode downward into engagement with cathode 9. Upon engagement of the electrodes, a circuit is completed from transformer |2 through contacts 20, resistor 2|, spring electrode cathode 9, coils of relays Hi and H3 and reactor 22 to the midtap of the secondary winding of transformer |2. A flow of alternating current accordingly occurs through such circuit, and relay l8 operates to open the contacts thereof, thereby deenergizing solenoid |6. Ignition electrode II is then withdrawn from cathode |9 under the action of spring Upon separation of the electrodes, the flow of current therebetween tends to continue in the form of a discharge, such discharge momentarily occurring in a direction depending upon the momentary polarity of transformer |2, and causing establishment of a cathode spot on the particular electrode which is negative with respect to the other electrode at the moment of their separation.

The cathode spot may thus be established on electrode H and if, at such instant circuit breaker I were closed and control electrodes 23 were positively energized, a current could flow from transformer 6 through anodes 8, electrode 1 spring resistor 2|, contacts 20, transformer |2, reactor 22, coils of relays l9 and I8 through line 4 and the load devices connected therewith back to transformer 6. Such flow of current would occur at the working voltage of the line and would therefore be apt to damage or even destroy the apparatus connected in the ignition circuit. Circuit breaker I being open and control electrodes 23 being negative, such flow of current cannot take place and the flow of current from cathode 9 to electrode ceases upon reversal of the voltage impressed therebetween. Relay l8 then returns to the position shown, and the operation of ignition electrode II is repeated until the separation of electrode II and cathode 9 occurs at an instant such that a cathode spot is established on the cathode.

When such cathode spot is established, an excitation discharge occurs from electrodes M to cathode 9, the discharge of the two excitation anodes combining at the cathode to form a flow of direct current which is maintained at a substantially uniform value as a result of the action of reactor 22. Such flow of current is of suincient magnitude to cause relay l9 to operate to close contacts 52. Closure of such contacts causes closing coil 53 to be energized from voltage divider 3|, so that circuit breaker l closes, and is maintained in the closed position by means of the latch maintained in engagement therewith by coil 54 energized from line 3. At such time, the flow of current through main anodes 8 of valve 2 is still prevented by the action of control electrodes 23. Relay I9 also opens the circuit of ignition electrode H at contacts 20, so

that the electrode becomes entirelyinoperative.

Relay i 9 also opens contact M, so that the control electrode of valve 42 is disconnected from the positive terminal of voltage divider 3i, and such control electrode becomes negative with respect to the associated cathode but is unable to render valve 42 non-conductive until the flow of currenttherethrough has been interruptedat contacts 39 of relay H. Relay l9 also opens contacts 3?, thereby removing the short circuit across the coil of relay 4%. Ihe relay therefore operates to close contacts at, thereby connecting windings 3% in a closed circuit with coil of relay ti and a portion of resistor 38. The magnetic energy stored in the cores of reactorstd then is gradually dissipated in theform of a flow of current of sufficient magnitude to cause relay M to continue its movement to open contacts 39 and thereby enable valve M to return to the non-conductive condition. The flow of current through windings 38 gradually decreases at a rate depending upon the amount of resistor 38 inserted in circuit therewith, with the result that the cores of the reactors are gradually desaturated and the inductance of the reactors gradually increases. The flow of current drawn by the working windings oi the reactors through resistors 34 thus gradually decreases, thereby causing a proportional decrease in the voltage drop caused by such current flow in resistors 34, As a result of such action,- the voltages of the phase portions of winding 23 gradually increase in magnitude and advance in phase. When the amplitude of such voltages is equal to thenegative potential of the neutral point of winding 2? with respect to the potential of cathode 9, each control electrode 23 periodically becomes positive at a comparatively late instant in the voltage cycle of the associated anode, and the'flow of current through valve 2 is released at the lowest possible voltage. Upon further increase of the magnitude of the voltages of winding 2? and further advance in their phase, the flow of current through each anode 8 is released at increasingly leading instants of the voltage cycle until windings 3% are without current, at which time the flow of current through valve 2 is released at the maximum possible voltage. Relay ll then returns to the position shown. The starting operation of valve 2 is then completed and the flow of current therethrough occurs at a predetermined voltage in relation with the voltage of line 3, and its intensity depends on the value of the impedance of the load connected with line t.

During such operation of valve 2, a sudden decrease of the load current in the valve to Zero, or even a sudden decrease from a high value to a low Value may cause the discharge in valve 2 to become unstable, so that the flow of current through both main anodes 3 and excitation anodes i l may be interrupted. The cathode is then no longer maintained in the conducting condition, and the excitation current cannot be reestablished until renewed operation of ignition electrode H. Upon such interruption of the excitation current, relay it returns to the position shown, thereby opening contacts 52. Circuit breaker 5 however, remains in the closed position because coil 5% is still energized from line 3 and maintains the latch in engagement with the cir-- cuit breaker. Contacts 3'! and M of relay is are again closed with the result that control electrodes 23 are again made negative with respect to cathode 8 in the manner above explained. Relay It also returns to the position shown to again initiate operation of ignition electrode 1 l in manner above explained.

If the control electrodes 23 were positive, the occurrence of a cathode spot on ignition electrode l i would then cause a flow of load current to occur through such ignition electrode, the ignition circuit, and the load circuit, thereby damaging or even destroying the ignition and excitation apparatus. Negative energization of control electrodes 23, however, will prevent this occurrence and, after one or more operations of ignition electrode H, a cathode spot is established at cathode 9 and the flow of excitation current from excitation anode l4 to cathode 9 is reestablished as above explained. Relay l9 then again operates and causes the flow of current through valve 2 to be released at a gradually increasing voltage.

Upon occurrence of a disturbance in the system resulting in an excessive flow of current through current transformer 49, the voltage appearing across the terminals of resistor d8 becomes of sufficient magnitude to cause the control electrode of valve d2 to become positive with respect to the associated cathode. Valve 12 thus becomes conductive and completes the connections between voltage divider 3i and windings 36, such connections now including the coil of relay ll. The cores of reactors 35 are thus rapidly saturated, resistor 38 being of a comparatively high resistance to impart a generally resistive character to the circuit of windings 36. As a result of the saturation of reactors 35, control electrodes 23' are brought to variable negative potentials with respect to the potential of cathode 9, thereby causing the flow of current through main anodes 8 to cease as is well known in the art. The core of relay M being energized, the relay operates, and its operating speed is so adjusted that con tacts it are closed only when the flow of current has already ceased through main anode 8. Upon closure of contacts 66, the reactors are gradually desaturated and the flow of current through main anodes B of valve 2 is reestablished at a gradually increasing voltage as above explained.

Although but one embodiment of the present invention has been illustrated and described, it

will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In combination, an electric valve having a main anode with an associated control electrode, a cathode, an ignition electrode and an excitation anode, a voltage source connectible with said ignition electrode and with said excitation anode and with said cathode, means including a source of control voltage for impressing on said control electrode potential of sign and magnitude effective to prevent initiation of the flow of current between said main anode and said cathode, and means responsive to the flow of current through said excitation anode and initiated by the operation of said ignition electrode for rendering inefiective the first said means.-

2. In combination, an electric valve having a main anode with an associated control electrode, a cathode, an ignition electrode and an excitation anode, a voltage source connectible with said ignition electrode and with said excitation anode and with said cathode, a switch for connecting said anode with said source, means including a source of control voltage for impressing on said control electrode potential of sign and magnitude effective to prevent initiation of the flow of current between said main anode and said cathode, and means responsive to the fiow of current through said excitation anode and initiated by the operation of said ignition electrode for rendering ineffective the first said means and for controlling the closure of said switch.

3. In combination, an electric valve having a main anode with an associated control electrode, a cathode and an excitation anode, a supply circuit and a load circuit interconnected by way of said anode and said cathode whereby said load circuit receives current at a voltage of predetermined value, a voltage source connectible with said excitation anode and said cathode to cause a flow of current therebetween, a source of control voltages for said control electrode, means for impressing between said control electrode and said cathode a voltage eiiective to prevent the flow of current between said main anode and said cathode, and means responsive to the flow of current between said excitation anode and said cathode for impressing between said control electrode and said cathode a voltage eifective to release the flow of current between said main anode and said cathode at a variable voltage gradually increasing to said predetermined value.

4. In combination, an electric valve having a main anode with an associated control electrode, a cathode and an excitation anode, a source of alternating current connected with said excitation anode and said cathode to cause a flow of rectified current therebetween, a source of negative unidirectional voltage connected with said cathode, a transformer having a primary winding connected with the first said source and a secondary winding connecting the second said source with said control electrode to periodically release the flow of current between said main anode and said cathode, and means responsive to failure of the flow of current between said excitation anode and said cathode for rendering said transformer ineffective to thereby cause said control electrode and the second said source to prevent the flow of current between said main anode and said cathode.

5. In combination, an electric valve having a main anode with an associated control electrode, a cathode and an excitation anode, a source of alternating current connected with said excitation. anode and said cathode to cause a flow of rectified current therebetween, a source of negative unidirectional voltage connected with said cathode, a transformer having a primary winding connected with the first said source and secondary winding connecting the second said source with said control electrode to periodically release the flow of current between said main anode and said cathode, and means responsive to failure of the fiow of current between said excitation anode and said cathode for reducing the amplitude of the voltage of said secondary winding to less than the value of the voltage of the second said source, whereby said control electrode is maintained at a variable negative potential to cause interruption of the flow of current between said anode and said cathode.

6. In combination, an electric valve having a main anode with an associated control electrode, a cathode and an excitation anode, a source of alternating current connected with said excitation anode and said cathode to cause a flow of rectified current therebetween, a source of negative unidirectional voltage connected with said cathode, a transformer having a primary winding connected with the first said source and a secondary winding connecting the second said source with said control electrode to periodically release the flow of current between said main anode and said cathode, impedance means in the connection between said primary winding and the first said source, a reactor connected with the first said source through said impedance means, and means responsive to failure of the flow of current between said excitation anode and said cathode for saturating the core of said reactor.

7. In combination, an electric valve having a main anode with an associated control electrode, a cathode, and an excitation anode, a source of alternating current connected with said excitation anode and said cathode to cause a flow of rectified current therebetween, a source of negative unidirectional voltage connected with said cathode, a transformer having a primary winding connected with the first said source and a secondary winding connecting the second said source with said control electrode to periodically release the fiow of current between said main anode and said cathode, and means responsive to failure of the flow of current between said excitation anode and said cathode for reducing the amplitude of the voltage of said secondary winding to less than the value of the voltage of the second said source, whereby said control electrode is maintained at a variable negative potential to cause interruption ofthe flow of current between said anode and said cathode and for gradually returning the voltage of said secondary winding to the normal value thereof upon restoration of the fiow of current between said excitation anode and said cathode.

8. In combination, an electric valve having a main anode with an associated control electrode, a cathode and an excitation anode, a source of alternating current connected with said excitationanode and said cathode to cause a flow of rectified current therebetween, a source of negative unidirectional voltage connected with said cathode, a transformer having a primary winding connected with the first said source and a secondary winding connecting the second said source with said control electrode to periodically release the flow of current between said main anode and said cathode, impedance means in the connection between said primary winding and the first said source, a reactor connected with the first said source through said means responsive to failure of the flow of current between said excitation anode and said cathode for saturating the core of said reactor to thereby render said transformer inefiective to thereby cause said control electrode and the second said source and prevent initiation of the flow of current between said main anode and said cathode and for gradually returning the core of said reactor to the normal magnetic condition thereof upon renewed flow of current between said excitation anode and said cathode.

9. In combination, an electric valve having a main anode with an associated control electrode, a cathode and an excitation anode, a supply circuit and a load circuit interconnected by way of said anode and said cathode whereby said load circuit receives current at a voltage of predetermined value, a voltage source connectible with said excitation anode and said cathode to cause a flow of current therebetween, a source impedance means, and

of control voltages for said control electrode, means for impressing between said control electrode and said cathode a voltage effective to release the flow of current between said main anode and said cathode, and means responsive to failure of the flow of current through said excitation anode and to the occurrence of flow of excessive current through said main anode for impressing between said control electrode and said cathode a voltage effective to prevent initiation of the flow of current through said main anode.

10. In combination, an electric valve having a main anode with an associated control electrode, a cathode and an excitation anode, a source of alternating current connected with said excitation anode and said cathode to cause a' flow of rectified current therebetween, a source of negative unidirectional voltage connected with said cathode, a transformer having a primary winding connected with the first said source and a secondary winding connecting the second said source with said control electrode to periodically release the flow of current between said main anode and said cathode, impedance means in the connection between said primary winding and the first said source, a reactorconnected with the first said source through said impedance means and having a saturating winding, an auxiliary electric valve connecting said saturating winding with the first said source, and means responsive to failure of the flow of current between said excitation anode and said cathode for rendering said valve conductive.

11. In combination, an electric valve having a main anode with an associated control electrode, a cathode, and an excitation anode, a voltage source connecting said excitation anode with said cathode to cause a flow of current therebetween, means exclusive of said source including a second voltage source for impressing between said control electrode and said cathode a voltage effective to release the flow of current between saidmain anode and said cathode, and

"means responsive to failure of the flow of ourrent between said excitation anode and said cathodeincluding a third voltage source for impressing between said control electrode and said cathode a voltage effective to prevent initiation of the fio-w of current between said main anode and said cathode.

12. In combination, an electric valve having a main anode with an associated control electrode, a cathode, and an excitation anode, a voltage source connecting said excitation anode with said cathode to cause a flow of current therebetween, means exclusive of said source including a second voltage source for impressing between said control electrode and said cathode a voltage effective to continually control the moments of initiation of the flow of current between said main anode and said cathode, and means responsive to failure of the flow of current between said excitation anode and said cathode including a third voltage source for impressing between said control electrode and said cathode a voltage effective to prevent initiation of the flow of current between said main anode and said cathode.

13. In combination, an electric valve having a main anode with an associated control electrode, a cathode, and an excitation anode, a voltage source connecting said excitation anode with said cathode to cause a flow of current therebetween, means exclusive of said source including a second voltage source for energizing said control electrode, and means including means responsive to failure of the flow of current between said excitation anode and said cathode for impressing between said control electrode and said cathode a voltage from the second said source effective to prevent initiation of the flow of current between said main anode and said cathode.

14. The combination with an electric valve comprising a main anode, a cathode, a control electrode, and an excitation anode, means comprising a source of potential for causing the flow of current between said cathode and excitation anode, means comprising a source of current for impressing on said control electrode potential of such sign and magnitude as to prevent the initiation of flow of current between said main anode and cathode, and means comprising a source of current for impressing on said control electrode potential of such sign and magnitude as to render ineifective the second said means, of means operable responsive to the said flow of current between said cathode and said excitation anode for rendering eifective the third said means.

FRANZ MERTENS.

CERTIFICATE OF CORRECTION.

Patent No. 2,109,865.. March 1, 19 8.

FRANZ MERTENS,

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page h second column, line 59, claim 8, for .to" read and; line 61, same claim, for and read to; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5d day of May, A. D. 1958.

(Seal) Henry Van Arsdale,

Acting Commissioner of Patents 

